ADE7753 View Datasheet(PDF) - Analog Devices
Part Name
Description
MFG CO.
'ADE7753' PDF : 60 Pages View PDF
ADE7753
LAENERGYIB(expected) =
INT(CFIB(expected ) × LINECYCIB /2 × PERIOD × 8 /CLKIN × (CFDEN + 1))
The calculated Wh/LSB ratio for the active energy register,
using Equation 39 is 6.378 × 10−4:
1
Wh
LSB
=
(489 +1)
3.200 imp/Wh
=
6.378 ×10 −4
Watt Offset
Offset calibration allows outstanding performance over a wide
dynamic range, for example, 1000:1. To do this calibration two
measurements are needed at unity power factor, one at Ib and
the other at the lowest current to be corrected. Either
calibration frequency or line cycle accumulation measurements
can be used to determine the energy offset. Gain calibration
should be performed prior to offset calibration.
Offset calibration is performed by determining the active
energy error rate. Once the active energy error rate has been
determined, the value to write to the APOS register to correct
the offset is calculated.
AENERGY Error Rate × 235
APOS = −
(49)
CLKIN
The AENERGY registers update at a rate of CLKIN/4. The twos
complement APOS register provides a fine adjustment to the
active power calculation. It represents a fixed amount of power
offset to be adjusted every CLKIN/4. The 8 LSBs of the APOS
register are fractional such that one LSB of APOS represents
1/256 of the least significant bit of the internal active energy
register. Therefore, one LSB of the APOS register represents 2−33
of the AENERGY[23:0] active energy register.
The steps involved in determining the active energy error rate
for both line accumulation and reference meter calibration
options are shown in the following sections.
Calibrating Watt Offset Using a Reference Meter Example
Figure 82 shows the steps involved in calibrating watt offset
with a reference meter.
SET ITEST = IMIN, VTEST = VNOM, PF = 1
MEASURE THE % ERROR BETWEEN THE
CF OUTPUT AND THE REFERENCE METER
OUTPUT, AND THE LOAD IN WATTS
CALCULATE APOS. SEE EQUATION 49.
WRITE APOS VALUE TO THE APOS
REGISTER: ADDR. 0x11
02875-A-008
Figure 82. Calibrating Watt Offset Using a Reference Meter
For this example:
Meter Constant:
MeterConstant(imp/Wh) = 3.2
Minimum Current:
Load at Minimum Current:
CF Error at Minimum Current:
CF Numerator:
CF Denominator:
Clock Frequency:
IMIN = 40 mA
WIMIN = 9.6 W
%ERRORCF(IMIN) = 1.3%
CFNUM = 0
CFDEN = 489
CLKIN = 3.579545 MHz
Using Equation 49, APOS is calculated to be −522 for this
example.
CF Absolute Error = CFIMIN(nominal) − CFIMIN(expected)
(50)
CF Absolute Error =
MeterConstant(imp/Wh)
(%ERRORCF(IMIN)) × WIMIN ×
3600
(51)
CF Absolute Error =
⎜⎝⎛
1.3%
100
⎟⎠⎞
×
9.6
×
3.200
3600
=
0.000110933
Hz
Then,
AENERGY Error Rate (LSB/s) =
CF Absolute Error × CFDEN +1
(52)
CFNUM +1
AENERGY Error Rate (LSB/s) =
0.000110933 × 490 = 0.05436
1
Using Equation 49, APOS is −522.
APOS = −
0.05436 × 235
3.579545 ×106
= −522
APOS can be represented as follows with CFNUM and WDIV
set at 0:
APOS =
−
(%ERRORCF ( IMIN ) )
× WIMIN
×
MeterConstant(imp/Wh)
3600
×
(CFDEN
+
1) ×
235
CLKIN
Rev. C | Page 42 of 60
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